Constants not loaded by compiler

Question

I started studying POSIX timers, so I started also doing some exercises, but I immediately had some problems with the compiler. When compiling this code, I get some strange

Answer 1

Referring to the CLOCK_MONOTONIC not being defined problem:

As Caterpillar pointed out this is an eclipse bug, more precisely a CDT-Indexer bug with a workaround at eclipse bugs, comment 12